HPTLC-MS: a tool for the efficient dereplication of pentacyclic triterpenic acids from Platostoma rotundifolium (Briq.) A. J. Paton (umusékerasúka)

Abstract

Dereplication is a process that consists of identifying within complex mixtures(crude extracts or first separation fractions) all the bioactive or undesirable molecules (or families of molecules) already known thanks to their physico-chemical properties. Dereplication strategies are  very diverse depending on the starting material (plants, animals, microbes, insects or marine organisms), the analytical techniques chosen (chromatographic and/or spectroscopic), the type of compounds sought and the final goal pursued. As previous researches have shown that aerial parts of P. rotundifolium (Asteraceae) contained pentacyclic triterpene acids (PTAs) including ursolic, corosolic, tormetic, hyptadenic and jeremic acids, this work aims to make dereplication of these compounds in ethyl acetate extract of the plant without having to isolate them. For this, high performance thin layer chromatography (HPTLC) was coupled with mass spectrometry (MS) to be used in this dereplication process. As results, we found that Rf values of five PTAs contained in the plant extract corresponded exactly to those of  the five standards used. These Rf values were (in decreasing order) 0.40; 0.33; 0.16; 0.10 and 0.06 corresponding to ursolic, hyptadienic,  jeremic, corosolic and tormentic acids respectively. In addition , the HPTLC–MSfull scan mass spectra (of standards and corresponding compounds from the plant extract) showed the same quasi-molecular ion pics [M-H]- at m/z 455.4, 469.5, 487.4/487.5, 471.4 and 487.4, corresponding to the loss of one proton of ursolic, hyptadienic, jeremic, corosolic and tormentic acids respectively. In view of the interesting results and despite the fact that this technique is little used in the field of triterpenoids, we can affirm that HPTLC-MS is a powerful method in the analysis of natural products such as PTAs contained in the aerial parts of P. rotundifolium (Briq.) A. J. Paton.